New Kinematic Model for the Palos Verdes
and San Pedro Basin Fault Zones in Santa Monica Bay, Offshore Southern
California
Hogan, Phillip J.1, Aaron
Broughton1, Kevin Smith1, Mark Legg2, Tom
McNeilan1, Robert R. Male3 (1) Fugro
West, Ventura, CA (2) Legg Geophysical, Huntington Beach, (3) Woodside Natural
Gas, Inc, Santa Monica, CA
High resolution seismic and geotechnical
data collected for Woodside's OceanWay LNG project
allow an improved understanding of the offshore Palos Verdes
and San Pedro Basin fault zones in Santa Monica Bay. Both faults offset
Latest Pleistocene and likely Holocene strata. A broad zone of deformation
exists from the Shelfbreak down to the base of slope
at the northeast margin of Santa Monica Basin.
The Palos Verdes
fault zone on Santa Monica Shelf offshore LAX exhibits transtensional
structures, including numerous left-stepping en echelon horsts and grabens. Farther north, the main trace of
the Palos Verdes fault bends towards the west, more
closely paralleling the structural grain of the Transverse Ranges to
the north.
The San Pedro Basin fault exhibits transpressional features, including popups
and growth folding in late Quaternary strata.
The prehistoric Los Angeles River deposited a thick offlapping sequence of deltaic strata in northeastern Santa Monica Bay, which were
subsequently cut by NW-trending strike-slip faults. Santa Monica Shelf was
beveled off during glacially lowered sea levels 16-20k yBP.
The beveled upper surface of the deltaic sequence is overlain by an undeformed coarse gravel layer deposited by the prehistoric
Los Angeles River. The top of the
pre-Holocene gravel marker horizon is not offset or disrupted by faults
underlying most of the mainland shelf.
The collisional
boundary of the Peninsular Ranges and Continental Borderland Provinces with the Transverse
Ranges Provinces is thus characterized by both transpressional
and transtentional structures on Santa Monica Shelf
and Slope. A new kinematic model for this area is
presented.